Plant by your climate, not the calendar.

An “average last frost” of May 10 means that in half of years there is a frost after May 10. Tender transplants (tomatoes, peppers, basil, squash) should go out one to two weeks after the average, or earlier with row cover on hand. Hardy crops (peas, spinach, onions, brassicas) shrug off light frost and can go in weeks before.

In fall the average first frost is the date to work backward from: a 60-day bean sown 75 days before it gives you two weeks of picking. Low spots and open fields frost earlier than a city garden against a south wall — your guide's estimate is for your general location; adjust for your yard.

Seeds respond to the soil they sit in. Your guide shows the soil temperature at 6 cm for today; here is what it means:

• < 7°C (45°F)

  Too cold for most seeds. Peas, spinach and fava beans will sit and wait; others rot.

• 7–13°C (45–55°F)

  Cool-season crops germinate: peas, lettuce, spinach, radish, brassicas, onions, potatoes.

• 13–18°C (55–65°F)

  Most seeds germinate. Beans, corn, chard and carrots go in; transplant tomatoes when nights stay above 10°C.

• > 18°C (65°F)

  Warm-season seeds — squash, cucumbers, melons, okra — germinate fast. Lettuce and spinach start to bolt.

The hardiness zone tells you what survives winter; the ecological region tells you what the summer, the soil and the rain are like. A zone 6 garden in Toronto and a zone 6 garden in Kansas City share a winter low and almost nothing else. Every local guide names both and links to their regional pages.